Prepare the pre-dough: In a bowl, mix 100 g warm milk, 60 g flour, 35 g sugar, and 7 g fresh brewer's yeast. Cover with cling film and let rest in a warm place for 15 minutes.
Make the dough: Transfer the pre-dough to a larger bowl. Add 1 egg, 100 g warm milk, 30 g sugar, a pinch of salt, and 50 g melted butter. Mix well. Sift 400 g flour and add gradually, mixing first with a fork then with hands until smooth dough forms.
Let the dough rise: Cover the dough with cling film and let it rest for 1 hour in a warm place.
Prepare the filling: In a bowl, blend 200 g tworog cheese (or ricotta), 30 g sugar, 1 egg, 20 g raisins, and 1 teaspoon vanilla extract until smooth.
Shape and fill the vatrushka: Divide the dough into six equal pieces and form balls. Grease a baking tray with sunflower seed oil. Using the base of a glass, make holes in each dough ball. Place the filling into the holes. Brush the edges with a mixture of milk and egg yolk.
Bake: Bake in a static oven at 180°C (356°F) for 25 minutes.
Finish and serve: Dust the baked vatrushki with icing sugar and serve warm.